Pouring a 15" Pitch Lap (Part 1) for the 20" f/4.5 Telescope Mirror

[TalksWithDirt]

Your pitch might be really old, like millions of years old.

[OKMUNWURX]

Is the mirror blank already prefigured roughly I.E. It's radii is used to 'set' the shape of your grinding tools?

[tabhorian]

I'm curious about the four large notches in the edges of the mirror. What are they for and how are they used?

[datzfast]

is pitch like asphalt ?

[GordonWaite]

@datzfast Something like it. I think it is extracted from trees. I use Gugolz pitch, and it's refined specifically for optical fabrication. Thanks! Gordon